1. Field of the Invention
The present invention relates to a liquid ejection apparatus and an ejection abnormality determination method, and more particularly, to ejection abnormality determination technology for nozzles which eject liquid droplets onto an ejection receiving medium.
2. Description of the Related Art
An inkjet recording apparatus having an inkjet type of ejection head forms a desired image on a medium by ejecting ink from a plurality of nozzles provided in the ejection head. In this inkjet recording apparatus, if an ejection abnormality occurs due to blocking of a nozzle as a result of drying (increased viscosity) of the ink, or intermixing of air bubbles, foreign matter, or the like, into the nozzles or pressure chambers, then the quality of the image formed on the medium will deteriorate. In particular, in a full line type ejection head having a nozzle row of a width equal to or exceeding the printable width of the medium, if there is an ejection abnormality in a particular nozzle, banding (color non-uniformities) arises in a direction substantially perpendicular to the breadthways direction of the ejection head and the quality of the image formed on the medium deteriorates markedly.
Various methods have been proposed for determining ejection abnormalities in nozzles in an inkjet recording apparatus. For example, it is possible to determine a pressure abnormality in a pressure chamber and thus determine an ejection abnormality in that pressure chamber, by providing pressure sensors in the pressure chambers and using a method which measures the frequency characteristics of the pressure (pressure wave) obtained from the pressure sensors, or a method which measures the current and voltage waveforms, or level (peak) obtained from the pressure sensors.
In the inkjet head and inkjet recording apparatus described in Japanese Patent Application Publication No. 11-99646, measurement is made of the change over time in the amount of charge flowing into a piezoelectric element due to vibration of the piezoelectric element, and hence the pressure wave in the ink pressure chamber is ascertained and an increase in fluid resistance can be detected in cases where air bubbles are present in the ink flow channel or where dirt or the like is present.
However, in a method which measures the frequency characteristics of the pressure (pressure wave) in the pressure chamber, it is necessary to scan the frequency characteristics from a low frequency to a high frequency, and this means that processing of the measurement results becomes complicated and it is difficult to make a judgment in a short period of time. Furthermore, in a method which measures the current and voltage waveforms and voltage level obtained from the piezoelectric elements, pulse noises are often superimposed on the current and voltage waveforms and voltage level obtained from the piezoelectric elements, and therefore the determination results are liable to be affected by the noises.
In the inkjet head and the inkjet recording apparatus described in Japanese Patent Application Publication No. 11-99646, a noise component is liable to be superimposed on the pressure waveform (determination signal) obtained from the piezoelectric elements, and therefore the signal has a low S/N ratio and the ejection abnormality determination results are liable to be affected by noise.